4-Acetyl-piperazinium picrate

In the title salt, C6H13N2O(+)·C6H2N3O7 (-) (systematic name: 4-acetyl-piperazin-1-ium 2,4,6-tri-nitro-phenolate), the piperazin-1-ium ring has a slightly distorted chair conformation. In the picrate anion, the mean planes of the two o-NO2 and p-NO2 groups are twisted with respect to the benzene ring by 15.0 (2), 68.9 (4) and 4.4 (3)°, respectively. In the crystal, N-H⋯O hydrogen bonds are observed, linking the ions into an infinite chain along [010]. In addition, weak cation-anion C-H⋯O inter-molecular inter-actions and a weak π-π stacking inter-action between the benzene rings of the anions, with an inter-centroid distance of 3.771 (8) Å, help to stabilize the crystal packing, giving an overall sheet structure lying parallel to (100). Disorder was modelled for one of the O atoms in one of the o-NO2 groups over two sites with an occupancy ratio of 0.57 (6):0.43 (6).

Unexpected enzyme-catalyzed regioselective acylation of flavonoid aglycones and rapid product screening

Unprecedented regioselective acylation of flavonoid aglycones was achieved using Candida antarctica lipase B (CALB). The rapid screening of product formation was performed by the use of the high resolution phenol-type OH (1)H NMR spectral region recorded after the addition of picric acid.

Dibenzo-18-crown-6-picric acid-water (1/2/3)

In the crown ether ring of the title compound, C(20)H(24)O(6)·2C(6)H(3)N(3)O(7)·3H(2)O, the O-C(H(2))-C(H(2))-O torsion angles indicate a gauche conformation of the ethyl-eneoxy units, while the C-O-C-C torsion angles indicate planarity of these segments; the dihedral angle between the two benzene rings is 44.53 (13)°. In both picric acid mol-ecules, one of the nitro groups is twisted away from the attached ring. The mol-ecules are linked into chains along the b axis via inter-molecular O-H⋯O hydrogen bonds. In addition, the crystal structure is stabilized by C-H⋯O hydrogen bonds and π-π inter-actions [centroid-centroid distance between benzene rings = 3.5697 (16) Å].

Three-dimensional network in piper-azine-1,4-diium-picrate-piperazine (1/2/1)

In the title compound, C₄H₁₂N₂²⁺·2C₆H₂N₃O₇⁻·C₄H₁₀N₂, the piperazine-1,4-diium cations and piperazine mol­ecules lie on crystallographic inversion centres. In the crystal structure, inter­molecular N—H⋯O and N—H⋯N hydrogen bonds link the components to form two-dimensional layers parallel to the (001) plane. These layers are, in turn, connected by weak inter­molecular C—H⋯O hydrogen bonds and π–π stacking inter­actions [centroid–centroid distance between parallel aryl rings = 3.764 (2) Å, interplanar spacing = 3.500 (2) Å and ring offset = 1.387 (2) Å], forming a three-dimensional framework.

Spectroscopic studies on [(DD18C6H2)(HPA)2](PA)2 and [(DD18C6H2)(DDQ)2](DDQH)2 formed in the reaction of N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane with HPA and DDQ

The interaction of the mixed oxygen-nitrogen cyclic base, N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DD18C6) with pi-acceptors such as picric acid (HPA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has been studied spectrophotometrically in chloroform at 25 degrees C. The results obtained indicate the formation of 1:4 charge-transfer complexes with the general formula (DD18C6)(acceptor)4. The electronic and infrared spectra of charge-transfer complexes along with the (1)H NMR spectra were recorded and discussed. Based on the data obtained, the complexes were formulated as [(DD18C6H2)(HPA)2](PA)2 and [(DD18C6H2)(DDQ)2](DDQH)2. A general mechanism explaining the formation of the DDQ complex has been suggested.